Internal combustion engines such as, for example, diesel engines, gasoline engines, and gaseous fuel powered engines, combust a mixture of air and fuel to produce power. The amount of air and fuel, and the ratio of air-to-fuel introduced into a combustion chamber of the engine can affect power output, efficiency, and exhaust emissions of the engine. Typically, the amount of air introduced into the engine and the ratio of air-to-fuel is controlled by a number of different fluid handling components located in both the air induction and exhaust systems of the engine.
An engine often includes a turbocharger to increase a power density of the engine. A turbocharger includes a turbine, driven by exhaust of the engine, to rotate a compressor and pressurize air directed into the engine. Depending on an internal geometry setting of the turbine and/or compressor, more or less air will be compressed to a higher or lower pressure for a given rotation. A variable geometry turbocharger (VGT), often used with diesel engines, is capable of altering the direction of exhaust flow to optimize turbine response. A VGT includes adjustable vanes within the turbine to adjustably direct exhaust flow radially inward toward turbine blades. It is common for a control system to command an actuator to change the angle of the vanes to optimize operation of the turbine. Changing the angle of air flow increases or decreases the speed of the turbocharger with a given amount of exhaust flow. Although this system can be successfully implemented, failure of the turbocharger due to excessive turbo speed my occur when the actuator is slow to adjust the movable vanes into a position that will decrease turbocharger speed. Hence, turbocharger failure may be caused by excessive energy passing through the turbocharger in response to a slow reaction by the actuator.
One attempt to minimize the likelihood of turbocharger failure has been described in U.S. Pat. No. 6,192,867 (the '867 patent) to Fenchel et al. The '867 patent describes a method and device for protecting a turbo-supercharger by determining a limit value for the fuel quantity metered to the engine from an intake air pressure, as derived from a program map. Determination of the intake air pressure does not require a sensor, because it is derived from a program map based on a function of charging pressures, engine speed, and a fuel quantity preset corresponding to an accelerator position. Reducing the fuel quantity decreases the overall energy in the exhaust conduit prevailing on the turbine of the turbocharger. As a result, the '867 patent is able to prevent the turbocharger from reaching a critical turbocharger speed.
Although the '867 patent may help reduce the likelihood of turbocharger failure due to excessive turbine speed, it may be overly complex and limited. The '867 patent is complex because the intake air pressure must be determined based on numerous input values. That is, it may be possible for the air pressure to be low and yet turbo speeds to be excessive. The '867 patent's derivation of intake air pressure may not accurately correspond to the actual speed of the turbocharger. The '867 patent is limited because it does not consider the effects of turbocharger failure when using a variable geometry turbocharger that includes an exhaust flow control device. That is, the '867 may be inapplicable to a turbocharger including a VGT.
The disclosed control system is directed to overcoming one or more of the problems set forth above.